JP2001-239861A and JP2002-192996A respectively disclose a power seat slide apparatus for a vehicle, which adjusts a position of a vehicle seat by sliding an upper rail relative to a lower rail by means of a driving force of an electrical drive source. As illustrated in FIGS. 4A-4B, each disclosed power seat slide apparatus for the vehicle includes a lower rail 81, an upper rail 82, a nut member 83, a screw shaft 84, and a gear box 85. The lower rail 81 is fixed to a vehicle floor, the upper rail 82 is slidably supported by the lower rail 81 and supports the vehicle seat, the nut member 83 is fixed to the lower rail 81, the screw shaft 84 is screwed together with the nut member 83, and the gear box 85 is fixed to a front end part of the upper rail 82 and transmits the driving force of the electrical drive source to the screw shaft 84.
The gear box 85 includes a gear housing 86 made of resin, a support bracket 87, and a plate 88. The gear housing 86 is sandwiched and held between the support bracket 87 and the plate 88. Further, the gear housing 86 of the gear box 85 houses, therein, a worm 91 and a helical gear (i.e., a worm wheel) 92. The worm 91 is provided on the electrical drive source and the helical gear 92 made of resin is fixed to a front edge portion of the screw shaft 84 and engaged with the worm 91.
As illustrated in FIG. 4B, the helical gear 92 is fixed to the screw shaft 84 in such a manner that the helical gear 92 is held between a washer 93 and a nut 94. The washer 93 made of metal is engaged with a stepped portion 84b of the screw shaft 84 and the nut 94 is fastened by means of a bolt portion 84a (ref. FIG. 4A) of the screw shaft 84 extending through the gear box 85. The washer 93 prevents the helical gear 92 made of resin from being directly contacted with the stepped portion 84b and deformed at the time of fastening the nut 94. A support bracket 87 is fixed to the upper rail 82 by means of a rivet 95 at plural mount portions 87a (only one mount portion 87a is illustrated in FIG. 4A) protruded along the upper rail 82 while contacting with a front end surface of the upper rail 82 and the gear box 85.
An end portion of the helical gear 92 contacting with the washer 93 forms a cylindrical shaft portion 92a. The shaft portion 92a of the helical gear 92 is supported by means of a bearing portion 86a of the gear housing 86. More particularly, the screw shaft 84 is rotatably supported about an axis and immovably supported in an axial direction by means of the gear box 85 (the gear housing 86) fixed to the upper rail 82 through the helical gear 92.
With the configuration of the disclosed power seat slide apparatus for the vehicle, in a condition where the screw shaft 84 provided with the helical gear 92 is rotated by rotary activating the worm 91 by means of the electrical drive source, the screw shaft 84 moves in the axial direction relative to the nut member 83 fixed to the lower rail 81. In consequence, the upper rail 82 slides relative to the lower rail 81, and the position of the vehicle seat relative to the vehicle floor is adjusted.
However, with the configuration of the disclosed power seat slide apparatus for the vehicle, with reference to FIGS. 4A-4B, an insert hole 87b of the support bracket 87, to which a front end portion of the screw shaft 84 is idly inserted, and the washer 93 in the axial direction are arranged in overlapped manner. More particularly, a part of an inner wall surface of the insert hole 87b is overlapped with the washer 93 in an outer diameter direction of the washer 93. Therefore, in a condition where the screw shaft 84 rotates with the washer 93, when the washer 93 and the insert hole 87b are interfered with each other, a sound caused by a contact between metals may be generated.
Further, in a condition where the insert hole 87b is configured with a larger inner diameter in order to prevent an interference between the insert hole 87b and the washer 93, a sufficient thickness of the support bracket 87 cannot be ensured as illustrated in FIG. 5. In consequence, the support bracket 87 may lack appropriate strength.
A need thus exists to provide a power seat slide apparatus for a vehicle, which ensures an appropriate strength thereof while restricting a sound.